1. Field of the Invention
The present invention relates to a photoelectric sensor capable of automatically adjusting one or both of a projected light power and a received light conversion factor (for example, a received light amplification factor).
2. Description of the Related Art
A product generally recognized as a photoelectric sensor is categorized as a device which projects light to a detection region, receives light transmitted through the detection region or light reflected by the detection region and acquires information on the presence or absence of an object and, if present, characteristics and geometrical parameters of the object on the basis of an amount of the received light. Since general purpose photoelectric sensors are installed in various conditions and used for various kinds of objects as a detection target, there has been conventionally known a photoelectric sensor wherein adjustments are performed on a projected light power and a received light amplification factor in a situation where a target is actually placed in a detection region to perform sensitivity adjustment thereof so as to obtain a proper detection value and, furthermore, trial detection is performed by altering a position of a detection target, for example, to thereby obtain a detection value and to, on the basis of the detection value, determine a threshold value for discriminating between detection values (see Japanese Unexamined Patent Publication No. 5-206820 (1993), for example).
In such a way, in a photoelectric sensor, determined based on actual data are a sensitivity adapting a situation in a detection region for a detection value, and a threshold value for evaluation and discrimination of an obtained detection value. In order to facilitate the adjustment operations for the determinations, there has been known a photoelectric sensor which displays a detection value and a threshold value in numerical value (see Japanese Unexamined Patent Publication No. 9-252242 (1997), for example).
There has also been known a photoelectric sensor of which a background level is stored as a zero reset reference value to display a remainder obtained by subtracting the zero reset reference value from a detection value in order to ensure quite obvious recognition of whether a displayed detection value corresponds to the background or to a detection target itself, wherein a detection value that is obtained in a state of background detection, which is not zero, is presented as zero in numerical value display (see Japanese Unexamined Patent Publication No. 2001-124594).
A detection value of a general purpose photoelectric sensor is evaluated as a relative value on an arbitrary scale suitable for a usage situation thereof, which is dissimilar to a case of a measuring instrument having a purpose to display a measured physical value (for example, a distance) using a unit therefor (for example, mm). Various light intensities of received light are observed in respective usage situations. Therefore, a sensitivity to adapt a situation in a detection region for a detection value can be adjusted on the basis of actual data so as to obtain the detection value in a proper range. There are also encountered variations in fabrication parameters and variations in installment conditions. With such circumstances, in a case where plural photoelectric sensors are prepared for use, sensitivities of the respective devices do not coincide with each other, which is generally not required to do so. A threshold value is adjusted on an individual device based on actual data after a sensitivity is determined.
In a case where plural photoelectric sensors are applied in the same usage situation, there has been a desire that after a first one is adjusted based on actual data, the others are adjusted with results from the first one to reduce time and labor. Such a requirement can also occur in a case where multiple photoelectric sensors are used in spatially parallel arrangement or in a case where photoelectric sensors are built in respective mass produced other apparatuses. For conventional photoelectric sensors, in a similar way to adjustment in the case of a photoelectric sensor that has been adjusted in the first place, individual adjustment with time and labor also have had to be conducted on a second photoelectric sensor and the others subsequent thereto.
Even in a case where a single photoelectric sensor is used alone, a case has arisen in which it is insufficient to apply only an automatic adjustment function (a teaching function) for a sensitivity and a threshold value. That is, even if a user of a photoelectric sensor can use the automatic adjustment function for a sensitivity and a threshold value, there still remains a chance for the user to desire manual adjustment of at least a threshold value in order to optimize a detection condition. In a conventional photoelectric sensor, however, a problem has been pointed out that it is left up to the hardware of the device what detection value is obtained as a result of automatic adjustment for a sensitivity that is performed prior to manual adjustment, which makes a manual adjustment operation difficult in spite of the automatic adjustment.